Example 1: corr_pH - simple temperature correction of pH

Consider an RBRconcerto³ C.T.D.pH logger. Without temperature correction, the pH output from Channel-4 would be a simple linear function of the raw data:

where R is the normalized voltage ratio from Channel-4 monitoring the pH sensor, c0, c1 are the core coefficients of the linear equation, and pHraw is the uncorrected output in pH units.

The parameter pH is well known to have a dependence on temperature, so a more accurate value is obtained if the compensated version of the equation is used. This is typically expressed in a form such as:

Casting this into the form used by the logger, corr_ph, is simple:

where

pHraw is c0 + c1 * R as before, now an intermediate variable in the equation,
x0 corresponds directly in value to the constant "Kph",
x1 is the calibration pH "pHcal", generally 7.0,
x2 is the calibration temperature 'Tcal' in °C,
n0 is the index of the temperature channel (2 in this example),
value(n0) is the final output value of the temperature channel in °C,
pHcorr is the corrected output in pH units.

Note that this equation is for the output from Channel-4, so the source of the primary raw data R is implicitly Channel-4: there is no n index to specify where the raw data originates.

Examples

CODE

>> calibration 4 type
<< calibration 4 type = ph__02

Confirm the channel type.

CODE

>> calibration 4 datetime = 20171201000000, c0 = 15.23461, c1 = -0.198743

Set the core coefficients.

CODE

>> calibration 4 datetime = 20171201000000, x0 = -0.00302, x1 = 7, x2 = 24.943

Set the cross-channel correction coefficients.

CODE

>> calibration 4
<< calibration 4 type = ph__02, datetime = 20171201000000, c0 = 15.23461, c1 = -0.198743, x0 = -0.00302, x1 = 7, x2 = 24.943, n0 = 2

Request confirmation of all calibration coefficients.